(1) Field of the Invention
The present invention relates to a granular calcium hypochlorite composition comprising calcium hypochlorite particles having an ellipsoidal cross-section, and a process for the preparation of this composition.
A granular calcium hypochlorite composition is used for sterilizing and disinfecting water, and especially is used in a large quantity for sterilizing the water of a swimming pool.
Note, the reference to a particle having an ellipsoidal cross-section, as used in this specification, denotes a spheroidal particle or a columnar particle having both ends rounded, which is ellipsoidal, and has a short diameter and a long diameter in section in the direction of the long axis thereof.
(2) Description of the Related Art
As the shape of the granular calcium hypochlorite composition, there are known an indeterminate pulverized shape having sharp edges, a columnar shape, and a spherical shape.
Processes for the preparation of a granular calcium hypochlorite composition have been disclosed as follows: U.S. Pat. No. 2,195,754 proposes a process in which a partially dried calcium hypochlorite composition is compression-molded into a sheet between heavy rolls, the sheet is pulverized, and the particle size is adjusted to obtain an inderminate pulverized granular calcium hypochlorite composition; U.S. Pat. No. 2,195,755 discloses a process in which the water content is adjusted to 28 to 36%, the composition is compression-extrusion-molded into a columnar molded body having a diameter of about 3 mm and a length of about 5.4 mm, and the molded body is dried to obtain a columnar calcium hypochlorite composition; and Examined Japanese Patent Publication No. 18,999/79 discloses a process in which a pulverized calcium hypochlorite composition is placed in a fluidized state, an aqueous slurry of calcium hypochlorite is sprayed onto the fluidized composition, and water is evaporated to cover particles in a fluidized bed with a solid layer of calcium hypochlorite, whereby a round granular calcium hypochlorite composition is prepared.
In these conventional granular calcium hypochlorite compositions, many problems arise with regard to the shape. More specifically, since the pulverization product has irregular and sharp edges, the edges are readily broken by friction between particles at the time of preparation, transportation or handling, and the composition is readily powdered and a fine dust formed. Furthermore, the flowability is very bad and problems arise at the time of packaging or during use.
Since the columnar product is obtained by extrusion molding, coarse portions and dense portions are present in the form of layers in each particle, and hence, the columnar product is easily broken. Moreover, since both ends of the columnar product are angular, the columnar product is broken by friction or impingement between particles at the time of preparation, transportation or handling to form a fine dust. Furthermore, the flowability is bad and problems arise at the time of packaging or during use.
As is apparent from the foregoing description, the pulverized product and the columnar product are both easily broken and formation of a fine dust is inevitable. This fine dust is scattered when an operator or user handles the composition, to cause health troubles such as irritation of the respiratory organs and irritation of the eyes. Moreover, because of a poor flowability, metering, and thus handling, become difficult.
On the other hand, the spherical product has no edges and a fine dust is not formed by friction or impingement between the particles. However, the flowability is too high and thus the metering is not satisfactory. Moreover, there is an unexpected problem of scattering caused by an impingement of particles when packaging. Namely, when the spherical products are spilled on the floor or the like, particles are dispersed over a broad area and it is very difficult to clear the particles away. Moreover, when the spherical product is scattered in a pool or the like, since the resistance is low, the dissolution speed differs in particles according to the particle size, and particles having a large diameter arrive at the bottom of the pool before dissolution to damage the bottom of the pool or the like.
Moreover, the follow:;ng problems arise in connection with the preparation of these granulation products. Namely, since the pulverized product is prepared by finely and mechanically pulverizing a sheet formed by pressing between rolls, a large quantity of a powdered product is formed as a by-product at the pulverizing step, and in some cases, the amount of the powdered product may be as large as 50% or more. The powdered product is removed by a classifier, and the powdered product, which is a fine dust, is collected and recycled to the compressing step. However, since the amount of the recycled powdered product is large, the size of the apparatus is large and the manufacturing cost is drastically increased. Furthermore, since the pulverized product is prepared through compression molding, the water solubility is low. The columnar product is formed by subjecting a wet composition to compression extruding using a die or the like. However, the molded body is extruded under a non-uniform pressure, due to the extrusion mechanism, and the molded body has coarse and dense portions. Accordingly, some portions have a low strength, and at the drying step, the molded body is broken or edges on both ends thereof are pulverized by friction or the like to cause powdering. Accordingly, collection and recycling of the powdered product become necessary, the steps become complicated, and the size of the apparatus becomes large, resulting in increase of the manufacturing cost.
The spherical product is prepared by using pulverized granules having a particle size adjusted by classification. An aqueous slurry of calcium hypochlorite is sprayed on this pulverized product when fluidized, and the pulverized product in the fluidized bed is covered with a layer of solid calcium hypochlorite formed by an evaporation of water from the slurry, to make the particles spherical. Accordingly, the step of preparing the pulverized product is essential. Further, since the amount of water evaporated from the aqueous slurry is large, a large quantity of energy is necessary for drying, and moreover, if the amount of water evaporated is large, a thermal decomposition of the calcium hypochlorite becomes greater and it is possible that the yield of the product will be reduced in this process. In addition, since the granulation and drying are simultaneously conducted in one step, the apparatus is complicated, the size thereof is increased, and the operation becomes difficult. In view of the preparation process, the particle size distribution in the spherical product is easily broadened and it is necessary to provide a sieving device and a device for pulverizing coarse particles.
The present inventors carried out research into the problems of the conventional products due to the shape thereof, and the problems involved in the preparation processes. As the result, it was found that a product having a spheroidal shape or a columnar shape having both ends rounded, which is ellipsoidal and has a short diameter and a long diameter in section in the direction of the long axis, i. e., the particles having an ellipsoidal section as referred to in this specification, is highly resistant to friction and compression and not readily powdered, and has a desirable flowability and excellent handling, metering and the like, and that when these particles having an ellipsoidal section are spilled, they are not widely dispersed. Namely, it was found that the particles having an ellipsoidal section do not have the problems of the conventional products. Furthermore, it was found that these particles can be prepared by extrusion-molding a wet composition of calcium hypochlorite to form a columnar molded body, and the molded body can be made ellipsoidal by rolling granulation, and according to this process, pulverization by breaking or friction is dramatically reduced at the drying step, where the molded body is subjected to severe conditions, and collection and sieving of the powdered product become substantially unnecessary, with the result that the recycling step can be omitted. It also was found that the particles of the obtained product have a uniform short diameter and the dissolution speed is high and uniform, irrespective of the long diameter, and that the particle size is uniform, the particles are rounded and exhibit an excellent appearance, and there are no coarse layer portions within the particles. The present invention was completed based on these findings.